The present invention relates to a porphyrin compound inclusive of a porphyrinato-zinc compound having a novel crystal form, an electrophotographic photosensitive member using such a porphyrin compound, and a process-cartridge and an electrophotographic apparatus including the photosensitive member.
Lasers currently used as exposure light sources in electrophotographic apparatus are predominantly semiconductor lasers having an oscillating wavelength around 800 nm or 680 nm.
In recent years, various approaches for realizing higher resolutions have been made so as to comply with increasing demands for output images of a higher image quality. The laser wavelengths are also concerned with realizing of the high resolution, and a shorter laser oscillation wavelength allows a smaller laser spot diameter facilitating a higher resolution electrostatic latent image formation.
Various proposals have been made for realizing shorter laser oscillation wavelengths.
One of such proposal is to reduce a laser light wavelength into a half by utilizing second harmonic generation (SHG) (JP-A 9-275242, JP-A 9-189930 and JP-A 5-313033). According to these proposals, GaAs laser and YAG laser already technically established and capable of high output power can be used as primary light sources, thus being able to realize a longer life or a larger output power.
Another proposal is to use wide-gap semiconductors, which allow a smaller size of device compared with the devices utilizing second harmonic generation. Lasers using ZnSe semiconductor (JP-A 7-321409 and JP-A 6-334272) and GaN semiconductor (JP-A 8-88441 and JP-A 7-335975) have been studied frequently in view of their high luminescence efficiency.
Such a semiconductor laser has posed difficulties in optimization of device structure, crystal growth conditions, electrodes, etc., and a long term oscillation at room temperature which is essential for commercialization has been obstructed due to occurrence of crystal defects, etc.
However, along with a technical innovation of substrates, etc., a report has been made on continuous oscillation for 1150 hours of a GaN semiconductor laser (at 50xc2x0 C.) in October 1997 from Nichia Kagaku Kogyo K.K., and a commercialization thereof is near at hand.
On the other hand, in electrophotographic photosensitive members used in conventional laser-equipped electrophotographic apparatus, charge-generating materials having a large absorption band and showing a practical sensitivity characteristic around 700-800 nm have been used, inclusive of non-metallic phthalocyanine, copper phthalocyanine and oxytitanium phthalocyanine, as specific examples.
However, such a charge-generating substance for long-wavelength lasers does not have a sufficient absorption band around 400-500 nm or, if any, is encountered with a difficulty in stably exhibiting a sufficient sensitivity due to a strong wavelength-dependence.
JP-A 9-240051 has disclosed an electrophotographic photosensitive member having a single layer-type photosensitive layer or a laminate-type photosensitive layer including a charge generation layer using a charge-generating material comprising an xcex1-form oxytitanium phthalocyanine as an electrophotographic photosensitive member suitable for a laser of 400-500 nm. According to our study, however, the use of the charge-generating material is accompanied with not only a low sensitivity but also a problem of resulting in an electrophotographic photosensitive member showing a large potential fluctuation in repetitive use due to a very large memory characteristic for light around 400 nm.
As for porphyrin compounds, JP-A 63-106662 has disclosed an electrophotographic photosensitive member using a 5,10,15,20-tetraphenyl-21H,23H-porphyrin compound in its charge generation layer, but has not succeeded in providing a commercial level of sensitivity characteristic.
Further, JP-A 5-333575 mentions tetrapyridyl-porphyrin as an example of an N-type conductive pigment to be used in combination with a phthalocyanine compound for providing a charge-generating material but contains no specific further description about the tetrapyridyl porphyrin.
For reference, syntheses of porphyrin compounds have been reported in, e.g., 1) H. Fisher and W. Glein, ANN. Chem. 521,157 (1936); 2) R. Rothemund, J. Amer. Chem. Soc., 58,525 (1936); 3) A. Adler, F. Longo, F. Kampas and J. Kim., J. Inorg. Nucl. Chem. 32,2442 (1970); and 4) A. Shamin, P. Worthington and P. Hambright, J. Chem. Soc. Pak. 3(1), p. 1-3 (1981).
An object of the present invention is to provide a porphyrin compound suitable for use as a charge-generating material in an electrophotographic photosensitive member.
A more specific object of the present invention is to provide a tetrapyridyl-porphyrin compound, particularly a tetrapyridyl porphyrinato-zinc compound having a novel crystal form.
Another object of the present invention to provide an electrophotographic photosensitive member showing a high sensitivity in a wavelength region of 380-500 nm by using such a tetrapyridyl-porphyrin compound.
Further objects of the present invention are to provide a process-cartridge and an electrophotographic apparatus equipped with such an electrophotographic photosensitive member.
According to the present invention, there is provided a 5,10,15,20-tetrapyridyl-21H,23H-porphyrinato-zinc compound having a crystal form selected from the group consisting of (a), (b) and (c) shown below:
(a) a crystal form characterized by peaks at Bragg angles (2xcex8xc2x10.2 deg.) of 9.4 deg., 14.2 deg. and 22.2 deg.,
(b) a crystal form characterized by peaks at Bragg angles (2xcex8xc2x10.2 deg.) of 7.0 deg., 10.5 deg. and 22.4 deg., and
(c) a crystal form characterized by peaks at Bragg angles (2xcex8xc2x10.2 deg.) of 7.4 deg., 10.2 deg and 18.3 deg., respectively in CuKxcex1-characteristic X-ray diffraction patterns.
According to another aspect of the present invention, there is provided an electrophotographic photosensitive member, comprising a support and a photosensitive layer disposed on the support, wherein the photosensitive layer contains a porphyrin compound having a structure represented by formula (1) shown below: 
wherein M denotes a hydrogen atom or a metal capable of having an axial ligand; R11 and R18 independently denote a hydrogen atom, an alkyl group capable of having a substituent, an aromatic ring capable of having a substituent, an amino group capable of having a substituent, a sulfor atom capable of having a substituent, an alkoxy group, a halogen atom, a nitro group or a cyano group; and A11 to A14 independently denote a hydrogen atom, an alkyl group capable of having a substituent, an aromatic ring capable of having a substituent or a heterocyclic ring capable of having a substituent with the proviso that at least one of A11 to A14 is a heterocyclic group capable of having a substituent.
The present invention further provides a process-cartridge and an electrophotographic apparatus equipped with the above-mentioned electrophotographic photosensitive member.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.